Different types of tools are used to perform hundreds of processing operations during semiconductor device fabrication. Most of these operations are performed in vacuum chambers at very low pressure. Wafers are introduced to the process chambers with wafer handling systems that are mechanically coupled to the process chambers. The wafer handling systems transfer wafers from the factory floor to the process chamber. These systems include loadlocks to bring the wafers from atmospheric conditions to very low pressure conditions and back, and robots to transfer the wafers to various positions. In performing the various wafer handling tasks, the wafer transfer robots use programmed coordinate information of the loadlocks, process modules, etc. At certain points, the position of a wafer may need to be adjusted to correct for wafer shifting during robot hand-off, robot movement or in a loadlock, process module or cassette.
Throughput—the number of wafers that is processed in a period of time—is affected by the process time, the number of wafers that are processed at a time, as well as timing of the steps to transfer the wafers. What are needed are improved methods and apparatuses for increasing throughput.